25.8 g of dimethyldichlorosilane, (CH3)2SiCl2, is completely hydrolysed and condensed to the linear silicone [(CH3)2SiO]_n with 80 % overall yield. Use atomic masses H = 1, C = 12, O = 16, Si = 28, Cl = 35.5. The mass of silicone obtained, in grams, to two decimal places, is

JEE Advanced levelNumerical answerDifficulty 3 of 3pb165

25.8 g of dimethyldichlorosilane, $(CH X_{3}) X_{2} SiCl X_{2}$ , is completely hydrolysed and condensed to the linear silicone $[(CH X_{3}) X_{2} SiO] X_{n}$ with 80 % overall yield. Use atomic masses H = 1, C = 12, O = 16, Si = 28, Cl = 35.5. The mass of silicone obtained, in grams, to two decimal places, is

Numerical answer type, answer in g, tolerance 0.01.

M ((CH X_{3}) X_{2} SiCl X_{2}) = 24 + 6 + 28 + 71 = 129 g/mol

, so 25.8 g is 0.200 mol. Each mole gives one

(CH X_{3}) X_{2} SiO

unit of mass

24 + 6 + 28 + 16 = 74 g/mol

, i.e. theoretical mass

= 0.200 \times 74 = 14.8 g

. With 80 % yield, mass

= 14.8 \times 0.80 = 11.84 g